Fibrotic livers demonstrate increased stiffness. This property can be exploited and measured using a newly developed ultrasound technology named Ultrasound Elastography (Transient Elastography (TE) or sonoelastography (SE). SE is performed by insonating the patient with a low energy, low amplitude, and low frequency shear wave created by focused ultrasound or by a vibrating probe on the skin. The small tissue movements produced by the propagated wave are then measured with ultrasound. The propagated wave travels faster with increasing fibrosis: the stiffer the tissue, the faster the shear wave propagates. A pulse-echo ultrasound acquisition allows measurement of the wave velocity and the results are presented as kilopascals (kPa). Tissue elasticity is calculated as the median of 10 measurements and ranges from 2.5 to 75 kPa with normal values around 5.5 kPa (Normal liver stiffness ranges between 3.3-7.8 kPa). Hepatic stiffness can be measured within a cylinder of tissue 1 cm wide and 4 cm in length producing an estimated sampling area that is 100 times greater than a biopsy. A meta-analysis assessing the capacity of transient elastography to diagnose moderate fibrosis found pooled estimates for sensitivity and specificity of 70% and 84% respectively. The mean area under the receiver operating characteristic curve (AUROC) for the diagnosis of significant fibrosis was 0.84% with an optimal cut-off of 7.6 kPa, and the diagnostic accuracy of SE for cirrhosis had an AUROC ranging from 0.90- 0.99 (mean AUROC 0.94) and cut-off from 9.0 to 26.5 kPa. The benefits of SE are that it is inexpensive, reproducible, painless, rapid (<10 min), easy to perform, and can be used for diagnosis, prognosis and monitoring disease progression. Limitations of sonoelastography are that measurements cannot be obtained in the presence of marked obesity, ascites, or unusually narrow intercostal spaces when externally applied vibrating shear wave generators are used.